1. Field of the Invention
The present invention is directed to an intake air pressure sensor assembly for an engine, and in particular, an air pressure sensor assembly for a fuel-injected engine which communicates with a controller for controlling the fuel injectors based on a detected intake air pressure.
2. Description of Related Art
In all fields of engine design, there is an increasing emphasis on obtaining more effective emission control, better fuel economy, and at the same time, continued high or higher power output. This trend has resulted in the substitution of fuel injection systems for carburetors as the charge former for internal combustion engines. Typically, fuel injection systems for internal combustion engines receive input from a variety of sensors included on the engine which are configured to output data which reflect the operating conditions of the engine. For example, a fuel-injected engine may include an engine speed sensor, an air temperature sensor, a throttle position sensor, an engine temperature sensor, and an air flow sensor. The controller for the engine monitors each of these sensors to determine the appropriate fuel injection timing and duration corresponding to the detected conditions. Thus, as the accuracy of the sensors and the processing of the data from the sensors is increased, so is the accuracy of the fuel injection duration and timing calculations and the emissions and the fuel efficiency of the engine.
Among the various types of data monitored by the controllers of fuel-injected engines, accurate determination of air flow into the engine poses a unique challenge. Although the flow of induction air into an engine is controlled by a throttle valve, it is imperative to determine the mass flow rate of air into the engine in order to determine the appropriate mass of fuel required to accurately produce the desired air/fuel ratio. In some applications, the mass flow rate of air into the engine is estimated by detecting the absolute pressure within the induction manifold (manifold absolute pressure or xe2x80x9cMAPxe2x80x9d) which is proportional to the total volume of air drawn into the engine. The absolute pressure is then used, in combination with other data collected from various other sensors, by the engine controller in order to calculate the mass air flow rate into the engine. Such calculations are known as volume-density computations or speed-density computations.
Recently, air flow meters have been used with fuel-injected engines which directly measure air flow rates of induction air into the engine. For example, known air flow meters include suspended-plate-type flow sensors, swinging-gate-type air flow sensors, and mass-flow sensors. However, these flow meters provide additional bulk and make engines more expensive to manufacture.
A need therefore exists for a less expensive fuel injection control system for an engine which accurately determines a flow rate of induction air into the engine.
One aspect of the present invention includes the realization that the timing during a combustion cycle, i.e., the crank angle position of a crankshaft, at which a minimum induction air pressure is generated within an internal combustion engine varies substantially in accordance with changes in engine speed and another engine operation characteristic. For example, in a four-cycle internal combustion engine, air is drawn into the respective cylinders when the intake valve is open and the piston moves downwardly within the cylinder, i.e., during the xe2x80x9cintake stroke.xe2x80x9d The intake stroke occurs once very two revolutions of the crankshaft. Thus, within the engine operation speeds between 1,000 rpm and 6,000 rpm, air is drawn through the induction system in pulses of a frequency from about 500 times per minute to 3,000 times per minute.
As induction air is drawn into the induction system, the absolute pressure generated in the induction system predictably falls in accordance with the vacuum generated by the downward movement of the piston. The actual mass flow rate attained by the induction air is affected by numerous conditions. For example, although the diameter of the cylinder and the stroke length of the piston of an internal combustion engine remain constant during operation, the atmospheric air pressure, temperature, and density may change in accordance with environmental conditions. Internal combustion engines having the same cylinder diameter and stroke length may also have differently configured induction systems with different aerodynamic resistance. Internal combustion engines also may incorporate variable valve timing for at least the intake valves, thus affecting the flow of induction air differently at different engine speeds. Accordingly, the minimum absolute pressure generated in the induction system is a result of numerous factors which can affect the mass flow rate of induction air through the induction system.
Significantly, it has been found that the timing at which the minimum pressure in the induction system is generated predictably varies according to the position of a throttle valve in the induction system, as well as engine speed. Additionally, it has been found that an output signal from a conventional air pressure sensor disposed in the induction system can be affected so as to output a signal that includes fluctuations but do not accurately reflect the air pressure in the induction system, thus generating a further unpredictable variation in the output signal from the pressure sensor. Thus, an engine constructed in accordance with a further aspect of the present invention includes an engine body defining at least one combustion chamber therein, a crankshaft rotatably journaled at least partially within the engine body, and an induction system configured to guide induction air into the combustion chamber. A pressure sensor assembly is configured to detect the pressure of an air flow in the induction system and to output a pressure signal indicative of the pressure detected. The engine also includes a charge former configured to supply a fuel charge for combustion in the combustion chamber. A controller controls the charge former as a function of at least the output signal of the pressure sensor. The engine also includes a smoothing system configured to smooth at least one of the pressure signals from the pressure sensor and the air flow in the induction system in the vicinity of the pressure sensor assembly.
By including a smoothing system that is configured to smooth at least one of the pressure signal from the pressure sensor and the air flow in the induction system in the vicinity of the pressure sensor assembly, the present invention provides more accurate data for the controller to use in controlling the charge former. Additionally, the higher level of accuracy achieved by including such a smoothing system, allows the controller to be manufactured with less sophisticated electronics, e.g., a less expensive processor.
As is known in the art, injecting an air-fuel mixture that is stoichiometrically perfect into an internal combustion engine provides the highest specific power output and the lowest emissions. It is also well known in the art that known internal combustion engines do not reliably produce air-fuel charges with stoichiometrically perfect air-fuel mixtures. Additionally, if an air-fuel charge combusted in an internal combustion engine is excessively xe2x80x9clean,xe2x80x9d i.e., there is too little fuel in the charge, the engine can be damaged through xe2x80x9cdetonation,xe2x80x9d for example. Thus, it is common in the art to configure some charge formers to produce xe2x80x9crichxe2x80x9d air-fuel charges. That is, some types of charge formers produce air-fuel charges that have more fuel than an air-fuel charge which is stoichiometrically perfect. Thus, these prior charge formers avoid damaging lean fuel charges by erring on the side of rich fuel charges, thereby protecting the engine but wasting fuel and discharging un-burnt fuel with the exhaust gases.
By constructing an engine in accordance with the present invention, more accurate fuel injection control is possible, thus allowing the engine controller to produce fuel charges that are more stoichiometrically correct, thus reducing fuel consumption and improving emissions of the engine.
Further aspects, features, and advantages of the present invention will become apparent from the detailed description of the preferred embodiments which follow.